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Two of NASA's Great Observatories, the Spitzer Space Telescope and the Hubble Space Telescope, have provided astronomers an unprecedented look at dusty planetary debris around stars the size of our sun.

This artist's concept depicts a distant hypothetical solar system, similar in age to our own. Looking inward from the system's outer fringes, a ring of dusty debris can be seen, and within it, planets circling a star the size of our Sun. This debris is all that remains of the planet-forming disk from which the planets evolved. Credit: NASA/JPL-Caltech/T. Pyle (SSC)

Spitzer has discovered for the first time dusty discs around mature,
sun-like stars known to have planets. Hubble captured the most detailed
image ever of a brighter disc circling a much younger sun-like star. The
findings offer "snapshots" of the process by which our own solar system
evolved, from its dusty and chaotic beginnings to its more settled
present-day state.

"Young stars have huge reservoirs of planet-building materials, while
older ones have only leftover piles of rubble. Hubble saw the reservoirs
and Spitzer, the rubble," said Dr. Charles Beichman of NASA's Jet
Propulsion Laboratory (JPL), Pasadena, Calif. He is lead author of the
Spitzer study. "This demonstrates how the two telescopes complement each
other," he added.

The young star observed by Hubble is 50 to 250 million years old. This
is old enough to theoretically have gas planets, but young enough that
rocky planets like Earth may still be forming. The six older stars
studied by Spitzer average 4 billion years old, nearly the same age as
the sun. They are known to have gas planets, and rocky planets may also
be present. Prior to the findings, rings of planetary debris, or "debris
discs," around stars the size of the sun had rarely been observed,
because they are fainter and more difficult to see than those around
more massive stars.

[LEFT: AU Microscopii] - A visible-light image of a debris disk around the red dwarf star AU Microscopii. Planets may be forming, or might already exist, within it. The disk glows in starlight reflected by tiny grains of dust created by the collisions of asteroids and comets. [RIGHT: HD 107146] - This is a false-color view of a planetary debris disk encircling the star HD 107146, a yellow dwarf star very similar to our Sun, though it is much younger (between 30 and 250 million years old, compared to the almost 5 billion years age of the Sun). The star is 88 light-years away from Earth. This is the only disk to have been imaged around a star so much like our own. Credit: NASA/ESA/J.E. Krist (STScI/JPL) & D.R. Ardila (JHU)Download larger image version here

"The new Hubble image gives us the best look so far at reflected light
from a disc around a star the mass of the sun," said Hubble study lead
author, Dr. David Ardila of the Johns Hopkins University, Baltimore.
"Basically, it shows one of the possible pasts of our own solar system,"
he said.

Debris discs around older stars the same size and age as our sun,
including those hosting known planets, are even harder to detect. These
discs are 10 to 100 times thinner than the ones around young stars.
Spitzer's highly sensitive infrared detectors were able to sense their
warm glow for the first time.

"Spitzer has established the first direct link between planets and
discs," Beichman said. "Now, we can study the relationship between the
two." These studies will help future planet-hunting missions, including
NASA's Terrestrial Planet Finder and the Space Interferometry Mission,
predict which stars have planets. Finding and studying planets around
other stars is a key goal of NASA's exploration mission.

NASA's Spitzer Space Telescope recently captured these infrared images of six older stars with known planets. The yellow, fuzzy clouds are disks of dust, or "debris disks," like the one that surrounds our own Sun. Though astronomers had predicted that stars with planets would harbor debris disks, they could not detect such disks until now. Credit: NASA/JPL-Caltech/C. Beichman (Caltech)Download larger image version here

Rocky planets arise out of large clouds of dust that envelop young
stars. Dust particles collide and stick together, until a planet
eventually forms. Sometimes the accumulating bodies crash together and
shatter. Debris from these collisions collects into giant
doughnut-shaped discs, the centers of which may be carved out by
orbiting planets. With time, the discs fade and a smaller, stable debris
disc, like the comet-filled Kuiper Belt in our own solar system, is all
that is left.

The debris disc imaged by Hubble surrounds the sun-like star called HD
107146, located 88 light-years away. John Krist, a JPL astronomer, also
used Hubble to capture another disc around a smaller star, a red dwarf
called AU Microscopii, located 32 light-years away and only 12 million
years old. The Hubble view reveals a gap in the disc, where planets may
have swept up dust and cleared a path. The disc around HD 107146 also
has an inner gap.

This is an artist's impression of the view from the vicinity of a hypothetical terrestrial planet and moon orbiting the red dwarf star AU Microscopii. Credit: NASA/ESA/G. Bacon (STScI)

Beichman and his colleagues at JPL and the University of Arizona,
Tucson, used Spitzer to scan 26 older sun-like stars with known planets,
and found six with Kuiper Belt-like debris discs. The stars range from
50 to 160 light-years away. Their discs are about 100 times fainter than
those recently imaged by Hubble, and about 100 times brighter than the
debris disc around the sun. These discs are also punctuated by holes at
their centers.

Both Hubble images were taken with the advanced camera for surveys. They
will be published in the Astronomical Journal and the Astrophysical
Journal Letters. The Spitzer observations are from the multiband imaging
photometer and will appear in the Astrophysical Journal.